The present invention relates to pressure-responsive systems and components and, more particularly, to apparatuses that sense fluid level or pressure and respond thereto by triggering a switching mechanism.
It is often desirable to know information about fluid level in tanks. Determining fluid level and controlling fluid level in tanks, such as in sewage tanks, water cisterns or tanks, and other fluid system and storage vessels, whether enclosed or open and exposed to the environment, has been done in a number of ways. Where applicable and accessible, visual readings can be taken. In some systems, though, visual readings are not desirable, since a response to the level indication is typically desired, such as to pump more fluid into the vessel or to discharge fluid from the vessel. In other situations, visual readings are not available due to lack of access. In addition, control systems are typically employed to respond to a fluid level indication, such as to operate a pump or a valved member in a gravity inflow or discharge arrangement, or to illuminate a light on an indicator panel representing the fluid level, e.g. Having a human operator make a visual fluid level reading and manually initiate this desired function may not be desirable due to the repetitive nature of the function or due to the inefficiency of having a human operator in the system.
These control or indicator functions are typically handled by electronic control systems which are responsive to one or more switches that are triggered by fluid level or pressure input. In sewage tanks, for example, it is well known to use multiple tilt style float switches to control fluid level. These may be mercury switches or rolling ball style switches, where a ball triggers a microswitch within the mechanism, that are triggered when the whole switch mechanism tilts downward toward a tethered connection a sufficient amount. These tilt style float switches are each attached via an anchor tether either directly to the vessel interior wall, or to a bar, rail, or other vertically disposed structural member within the vessel, such that a plurality of these tilt style float switches are disposed vertically with each one representing a unique elevation of fluid level within the vessel. They operate on a one-to-one ratio, that is, at the point they are triggered they are meant to represent that specific fluid level within the vessel. Numerous problems, however, have been encountered with these mechanisms.
Turbulent conditions within a fluid-holding vessel can negatively impact performance of float switch systems. Within a sewage tank, e.g., turbulence can result from fluidized material inflow, but more typically from pump-discharged fluid material exiting the tank. This turbulence can create undesirable eddies and waves within the tank that can cause tethered tilt style float switches to become entangled, thus preventing them and the system from proper operation. In addition, the turbulence within the tank can cause inadvertent switching (i.e., a switch to trigger prematurely or later than desired) and what is often referred to as xe2x80x9ccontact chatterxe2x80x9d of the switches within the tilt style float switch assemblies. Inadvertent switching can cause system inefficiency and degradation, such as from a false level reading or from a pump to turn on or off earlier or later than desired. Such contact chatter can cause the pump, which is responsive to the triggered switch, to cycle inadvertently on and off at a high rate, resulting in undue and undesirable system wear and operation.
Other problems that can result from tilt style float switches are due to the fact that they are disposed on the surface of the fluid material in the sewage tank, a highly corrosive and greasy environment. These tethered switches can become damaged from banging against each other and the tank wall during the turbulent system operation. In addition, the greasy outer surface of the tilt style float switches can cause them to intermittently adhere and even get stuck against the tank wall, thus affecting system performance and reliability. In addition, low pressure sewage system tanks in both residential and commercial use are often of corrugated side wall construction. These corrugations can serve as a series of mini ledges or shelves to the grease-covered tilt style float switches, thus facilitating their adherence and entrapment.
The tilt style float switches can also become corroded. Leaking mercury from some styles of these switches poses a serious environmental and health hazard. Non-mercury versions of the tilt style float switches can similarly be ruined by corrosion, such as of the contact or leads, thus rendering them inoperable.
Another type of known switching mechanism performs similarly to the typical ball float that operates the valve in a toilet, which floats with the fluid level and closes the valve when the tank is full after the toilet is flushed. In these switching mechanisms, the ball floats on the liquid and bumps switches on and off, but it can only act on a one-to-one ratio, that is, the ball float represents the actual liquid level when the switch is bumped and triggered, not some multiple thereof.
Electronic pressure transducers have been used to sense fluid pressure. These devices are disposed in the fluid and typically operate by direct pressure against a diaphragm area that changes its resistive value as the component strain changes. They require an electronic box to convert the circuit signals to analog relay outputs for use in controlling pumps, etc. Though reliable, these electronic pressure transducers and required electronics are expensive.
Another common problem with all of the aforementioned tilt style float switch, vertical ball float or electronic pressure transducer systems is in servicing these systems. Since they are disposed in sewage tanks or other fluid vessels, servicing them can be a messy, less than ideal, undertaking.
The present invention provides a new and unique pressure activated control apparatus and system that overcomes the above problems and others.
An improved pressure activated control apparatus is provided that includes a first resilient member having a first or outer surface exposed to the fluid and responsive to the fluid pressure to trigger one or more switches of a switching mechanism. It has a second or inner surface exposed to the inside of the apparatus that is sealed from the fluid. A force translation and switching mechanism is provided that responds to the force exerted by the pressure of the fluid on the outer surface of the first resilient member to trigger one or more switches within the apparatus. The pressure activated control includes a second resilient member that provides a biasing force against the force translation and switching mechanism in a direction opposite to the force exerted by the fluid pressure on the outer surface of the first resilient member. In this way, change in height of the fluid level within the vessel compared to movement of the force translation and switching mechanism is greater than one-to-one.
The apparatus of the present invention provides a reliable, affordable alternative to known tilt style float switches, vertical float switching assemblies and electronic pressure transducer-based systems used for, among other possibilities, determining fluid level or controlling fluid level in open or enclosed fluid holding vessels, such as fluid storage or septic tanks, cisterns, sump and sewage basins, and other fluid system and storage vessels. In one embodiment, the pressure activated control of the present invention is provided in an elongate, vertically disposed housing that can be connected to an interior side wall of a tank, cistern or other fluid-holding vessel, such that the first resilient member has an outer surface that is substantially always in contact with the fluid. The first resilient member can be a pliable rolling diaphragm made of durable nitrile rubber, or any other suitable material selected based on the environment it is to be exposed to, including chemical and thermal environments, e.g. The rolling diaphragm is in the shape of a bellofram, or a cup with a radially outwardly extending peripheral flange at its upper open end (i.e., it is top hat-shaped), that is sealed at its flange to the housing near a first or lower housing end. The rolling diaphragm acts together with a push cup, a rod and a plunger that are centrally disposed in the elongate housing to serve as a substantially zero friction piston to actuate or trip one or more switches, such as a plurality of microswitches.
In an embodiment, the second resilient member can be a spring of a selected spring constant, xe2x80x9ck,xe2x80x9d that is disposed within the housing between the push cup and an annularly disposed spring plate which is connected to the housing. The spring can be annularly disposed around the rod and provides a biasing force against the push cup and rolling diaphragm, such that for every lineal distance of movement of the piston assembly, which includes the rolling diaphragm, push cup, rod and plunger, vertically upward within the housing, a multiple greater than one times that lineal distance of incremental fluid level is being represented by that piston assembly movement. Simply changing the spring to one with a different spring constant k, allows for a different fluid level range to be sensed or controlled with the same pressure control apparatus. For example, one spring can give approximately eighteen inches of fluid level representation or control with about four inches of corresponding piston assembly travel, whereas a second spring can give forty-two inches of fluid level representation or control. Obviously, substituting a different spring (different k constant) will give a correspondingly different range of fluid level control.
In an embodiment, a plurality of microswitches are housed in a head portion of the housing, at a second or upper housing end, and are each adjustably and removably connected on an inventive switch track assembly such that each one is tripped at a different plunger vertical elevation within the housing, thereby allowing for adjustable fluid level control within the vessel. In one embodiment, the switch track assembly comprises a top piece and a bottom piece connected by four identical spaced switch mounting rails, or switch track rods. The microswitches are each connected to a switch coupler piece that snaps onto an adjacent pair of the rods, such that the switch trigger can be contacted by the plunger coming through a hole in the bottom piece of the switch track assembly in response to sensed fluid pressure on the overall piston assembly. Each switch coupler and corresponding microswitch pair can easily be snapped along the switch track rails making for an adjustable fluid level control system. In an embodiment, the switch track assembly can accommodate up to fourteen such commercially available microswitches each mounted on a removable switch coupler to two adjacent switch track rods.
Although one surface of the rolling diaphragm is meant to be continuously exposed to fluid material in the tank at a subsurface fluid level, the remaining interior of the housing is sealed from the fluid and can be connected to a source of fresh air, such as by a vent tube or line connected at some upper apparatus location to outside air external to the fluid vessel. In this way, the switches are not exposed to corrosive liquids or gases within the vessel and the volume of air displaced by the rolling diaphragm and piston assembly in response to a fluid elevation increase in the vessel can be vented. Correspondingly, the vent line serves as a source of fresh air brought into the apparatus when the fluid elevation within the vessel is decreased, such as by a pump discharge cycle, and the rolling diaphragm unrolls or relaxes with the piston assembly moving downward.
The housing may be made substantially from a combination of commercially available, off-the-shelf, standard sized PVC piping, couplers, reducers, aluminum bar stock, and the like, and from a minimum number of specially fabricated components (such as of molded ABS, Lexan(copyright) (General Electric Company) or other suitable plastic, or fabricated from another suitable material), thereby minimizing system cost. In an embodiment, four microswitches can be provided representing, from lowest to highest elevation along a switch track assembly: off, pump on one, pump on two, and an alarm, respectively. Such is a common set up in sewage tank systems, thereby making for easy retrofit of tilt style float switch sewage tank systems with the present invention. The inventive apparatus can simply replace the tilt style float switches and be wired to the existing control system. Servicing the system and adjusting the switches and corresponding fluid control levels can be done simply and in the field, without any tools. In another possible system embodiment for sensing fluid level and indicating the same, fourteen microswitches can be provided. Such a system could be employed to represent a series of fluid elevations on an indicator panel and have an alarm level, e.g. Of course, longer piston assemblies and switch track assemblies could be substituted allowing for more microswitches and more range of fluid level representation and control.
The pressure activated control apparatus and system of the present invention provide a reliable, affordable and easily serviceable means to trigger a switching apparatus in response to fluid pressure or level. No electric cords or components are submerged in the fluid. The fluid level can be adjustably controlled by the apparatus. The apparatus operates within its own enclosure envelope and senses fluid pressure at a subsurface fluid level, such that it is not susceptible to turbulent surface conditions or the greasy surface layer typically found in sewage tanks that is known to affect system performance and reliability.
Still further advantages of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments.